Detector of hidden wiring

Detector of hidden wiring

Many home craftsmen need a device that would help find hidden electrical wiring. You can make it using the diagram below (see picture)..


Analogues of semiconductor components:

- КТ315Б - BFP719, С945, 2SC1815

- КП103Д - 2N3329, 2N2842

- АЛ307Б - JLCPCB (LED, 10-15 am)

This hidden wiring detector eliminates the potential risk of a drill in the wire when drilling a wall, will allow you to trace the path of an electric cable in the wall and help in many other cases when it is necessary to detect hidden metalwork.
A section of wire or a metal rod with a diameter of about 5 mm and a length of 70 ... 90 mm is an antenna.

Scheme and principle of the hidden wiring detector

The principle of operation of the wiring detector circuit is as follows. On a bipolar transistor VT1 and VT3 a low-frequency multivibrator is assembled. Its operating frequency is mainly determined by the nominal capacitors, which are used as aluminum, niobium or tantalum electrolytic capacitors.

In the initial state, when the wiring detector antenna probe is far away from the hidden wiring, the field transistor VT2 is in the clipping mode. At the same time, on the resistor R4, which is included in the leakage circuit of the transistor VT2 (KP103D), the voltage falls to approximately 3.5 V. This captures the potential of the base VT3 at a level that keeps VT3 in the saturated state. In this case, the LED lights continuously. Transistor VT1 at this time to be in cut-off mode.
When the sensor probe antenna approaches the hidden wire of the wire, where the alternating potential of 220 V is maintained, the electrical component of the electromagnetic field of the network leads to an alternating potential equal to hundreds of milli-volt volts on the antenna input. In this case, the corresponding half-periods of the input signal open VT2, the current through the resistor R4 increases, and hence, increases and decreases the voltage on it. The VT3 base potential for the VT3 emitter becomes low by converting VT3 to clipping mode.

As a result, the LED detector flashes, signaling the presence of hidden wiring in this place.

Used material of the article L. Enikeev in the journal"Радіоаматор", №11, 2001р.